Components in a gas turbine engine may be exposed to relatively high temperatures and thus are often cooled. One cooling method that is often used is effusion cooling. With effusion cooling, a thin film of air may enter the component through cooling through holes formed in the component. The thin film of air removes heat by conduction and by preventing hot gases from impinging upon the component. Many times effusion cooled components, and more particularly the through holes themselves, tend to become obstructed when operated in certain environments. Thus, larger diameter through holes are sometimes used to prevent blockage. When using these larger diameter through holes, the hole density decreases to minimize total flow to cool the component. This decrease in hole density tends to create an irregular cooling pattern in the form of hot spots. This may also increase the occurrence of the cooling fluid mixing with hot gases and reduce protection of the component. Convective cooling within the through hole is further reduced as the wetted internal area decreases at constant flow when the through hole diameter is increased. All these factors can reduce the overall cooling effectiveness of the component.
Effusion through holes are also typically drilled at a shallow angle to reduce penetration and dilution of the cooling film into the hot gases. This phenomenon is enhanced when the cooling flow exhibits a high relative velocity relative to the ambient hot gases. A classical remedy to this problem is to slow the exiting cooling flow by diffusing it before it enters the hot gas area. Such diffusing through holes have been produced in the past by a variety of methods including laser percussion drilling, various forms of electric discharge machining, laser trepanning, or combinations thereof. While generally effective, these methods can create jets that retain a significant normal velocity component moving the cooling film away from the wall. Curved shaped cooling holes produced by EDM have been proposed but remain an expensive method to create an effusion cooling film on a component of a gas turbine engine.
Accordingly, there is a need for low cost percussion drilled shaped through hole and method of fabrication that provides for efficient cooling of the component.